U.S. patent application number 10/746400 was filed with the patent office on 2004-07-15 for method of manufacturing thin quartz crystal wafer.
This patent application is currently assigned to Nihon Dempa Kogyo Co., Ltd.. Invention is credited to Chiba, Akio, Kurosawa, Tamotsu, Ono, Kozo.
Application Number | 20040135467 10/746400 |
Document ID | / |
Family ID | 32708463 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040135467 |
Kind Code |
A1 |
Chiba, Akio ; et
al. |
July 15, 2004 |
Method of manufacturing thin quartz crystal wafer
Abstract
A method of manufacturing a thin quartz crystal wafer from a
quartz crystal block which is cut from a crystal body of synthetic
quartz crystal and has a flat principal surface, comprises the
steps of (a) converging a laser beam at a region in said quartz
crystal block at a predetermined depth from the principal surface
thereof to cause multiphoton phenomenon state, thereby breaking
Si--O--Si bonds of quartz crystal in said region to form voids in
said region, and (b) peeling said thin quartz crystal wafer from a
body of said quartz crystal block along said voids. The above
process is repeatedly performed on one quartz crystal block to peel
off a plurality of thin quartz crystal wafers successively from the
principal surface of the quartz crystal block. Each of the thin
quartz crystal wafers is divided into individual quartz crystal
blanks for making quartz crystal units.
Inventors: |
Chiba, Akio; (Saitama,
JP) ; Ono, Kozo; (Saitama, JP) ; Kurosawa,
Tamotsu; (Saitama, JP) |
Correspondence
Address: |
Patent Group
Choate, Hall & Stewart
Exchange Place
53 State Street
Boston
MA
02109-2804
US
|
Assignee: |
Nihon Dempa Kogyo Co., Ltd.
|
Family ID: |
32708463 |
Appl. No.: |
10/746400 |
Filed: |
December 26, 2003 |
Current U.S.
Class: |
310/310 ;
29/25.35; 310/366; 333/189 |
Current CPC
Class: |
Y10T 29/42 20150115;
Y10T 29/49005 20150115; C30B 33/00 20130101; Y10T 29/49002
20150115; H03H 9/19 20130101; Y10T 29/49798 20150115; C30B 29/18
20130101; H03H 3/02 20130101 |
Class at
Publication: |
310/310 ;
310/366; 333/189; 029/025.35 |
International
Class: |
H04R 017/00; H03H
009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2002 |
JP |
2002-380957 |
Claims
What is claimed is:
1. A method of manufacturing a thin quartz crystal wafer from a
quartz crystal block which is cut from a crystal body of synthetic
quartz crystal and has a flat principal surface, the method
comprising the steps of: (a) converging a laser beam at a region in
said quartz crystal block at a predetermined depth from the
principal surface thereof to cause multiphoton phenomenon state,
thereby breaking Si--O--Si bonds of quartz crystal in said region
to form voids in said region; and (b) peeling said thin quartz
crystal wafer from a body of said quartz crystal block along said
voids.
2. The method according to claim 1, wherein said steps (a) and (b)
are repeatedly carried out on said quartz crystal block from which
said thin quartz crystal wafer has been peeled, for thereby peeling
a plurality of thin quartz crystal wafers successively from the
principal surface of said quartz crystal block.
3. The method according to claim 2, wherein the principal surface
of said quartz crystal block is polished after said thin quartz
crystal wafer has been peeled therefrom, and then said step (a) is
carried out on said quartz crystal block.
4. The method according to claim 1, wherein said step (b) comprises
the step of heating said quartz crystal block.
5. The method according to claim 1, wherein said step (b) comprises
the step of immersing said quartz crystal block in an etching
solution.
6. The method according to claim 1, further comprising the steps
of: polishing said thin quartz crystal wafer; and dividing said
polished thin quartz crystal wafer into individual crystal
blanks.
7. The method according to claim 6, wherein each of said crystal
blanks is an AT-cut crystal blank.
8. The method according to claim 1, further comprising the steps
of: polishing said thin quartz crystal wafer; forming excitation
electrodes and extension electrodes in regions, corresponding
respectively to individual crystal blanks, on both principal
surfaces of said polished thin quartz crystal wafer; and dividing
said thin quartz crystal wafer with said excitation electrodes and
extension electrodes formed thereon into said individual crystal
blanks.
9. The method according to claim 8, wherein each of said crystal
blanks is an AT-cut crystal blank.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of manufacturing a
thin quartz crystal wafer from a crystal body of synthetic quartz
crystal, and more particularly to a method of manufacturing a thin
quartz crystal wafer using a laser beam.
[0003] 2. Description of the Related Art
[0004] Synthetic quartz crystal that is produced by growing quartz
crystal according to hydrothermal synthesis or the like is known as
a major material of electronic components typified by quartz
crystal units. A quartz crystal unit comprising a quartz crystal
blank cut from synthetic quartz crystal and hermetically sealed in
a casing is used as a frequency control element in an oscillator or
a filter. An AT-cut quartz crystal blank whose resonant frequency
is inversely proportional to its thickness is widely used in such a
crystal unit. A crystal blank is generally manufactured by cutting
a thin quartz crystal wafer having a desired thickness. In recent
years, as the communication frequency is as high as 100 MHz or
higher, for example, a crystal blank used as a quartz unit has a
thickness of about 18 .mu.m or less. Efforts have been made to
develop a process of manufacturing such a crystal blank.
[0005] FIGS. 1A to 1C show successive steps of a conventional
process of manufacturing a thin quartz crystal wafer. Thin quartz
crystal wafer 1 is cut from quartz crystal block 2 in the form of a
rectangular parallelepiped having flat surfaces. As shown in FIGS.
1A to 1C, if an AT-cut crystal blank is to be finally cut out, then
quartz crystal block 2 is cut from a crystal block of synthetic
quartz crystal along predetermined orientations (X-, Y'-, and
Z'-axes) of quartz crystal. The X-, Y'-, and Z'-axes refer to
crystalline axes that are crystallographically determined for
quartz crystal. Quartz crystal block 2 is cut by a wire saw or a
blade saw along line A-A in FIG. 1A to produce relatively thick
quartz crystal wafer 3 having a thickness along the Y'-axis. The
thickness of thick quartz crystal wafer 3 is of about 350 .mu.m.
Thereafter, thick quartz crystal wafer 3 is polished or ground into
thin quartz crystal wafer 1 having a prescribed thickness. If a
crystal blank for use in a 100 MHz crystal unit is to be produced
from thin quartz crystal wafer 1, thin quartz crystal wafer 1 has a
thickness of about 18 .mu.m. Then, thin quartz crystal wafer 1 is
cut into individual crystal blanks along line B-B and line C-C in
FIG. 1C by photolithographic etching.
[0006] Finally, as shown in FIG. 2, exciting electrodes 5 and
extension electrodes 6 are formed on respective principal surfaces
of crystal blank 4, extension electrodes 6 extending from
respective exciting electrodes 5 to an end of crystal blank 4 and
having portions folded back onto the other principal surfaces
across the end of crystal blank 4. Crystal blank 4 with exciting
electrodes 5 and extension electrodes 6 mounted thereon is
hermetically sealed in a casing, and predetermined electric
connections are made to extension electrodes 6, thus completing a
crystal unit.
[0007] According to the above manufacturing process, however, thin
quartz crystal wafer 1 is obtained from a thick quartz crystal
wafer having a thickness of several hundreds .mu.m by polishing or
grinding in the unit of .mu.m. Therefore, the manufacturing process
produces material wastes and is low in productivity. Since a wafer
cut by the machining process using a wire saw or a blade saw has a
thickness ranging from 200 to 400 .mu.m as a lower limit, it is
necessary to polish or grind thick quartz crystal wafer 3 in order
to produce thin quartz crystal wafer 1 therefrom.
[0008] A technique known as "stealth dicing" has been proposed for
producing a thin silicon semiconductor wafer having a thickness of
about 30 .mu.m without polishing or grinding. This technique
employs a laser beam having a wavelength that is transmissive with
respect to a semiconductor wafer to be processed thereby. The laser
beam is converged inside the semiconductor wafer to cause
multiphoton absorption in the converged area, thereby forming an
internally modified region from which the semiconductor wafer
starts to be divided. Details of stealth dicing are disclosed in
Takaoka Hidetsugu, "Principles and features of stealth dicing
technique optimum for dicing ultrathin semiconductor wafers",
Electronic materials (Denshi Zairyou in Japanese) (ISSN 0387-0774),
Vol. 41, No. 9, pp. 17-21, September 2002, and Japanese laid-open
patent publication No. 2002-205181 (JP, P2002-205181A).
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a method
of manufacturing a thin quartz crystal wafer with increased
productivity, with reduced quartz crystal wastes which is caused by
polishing and grinding.
[0010] Another object of the present invention is to provide a
method of manufacturing a crystal unit inexpensively using a method
of manufacturing a thin quartz crystal wafer with increased
productivity.
[0011] The objects of the present invention can be achieved by a
method of manufacturing a thin quartz crystal wafer from a quartz
crystal block which is cut from a crystal body of synthetic quartz
crystal and has a flat principal surface, the method comprising the
steps of (a) converging a laser beam at a region in the quartz
crystal block at a predetermined depth from the principal surface
thereof to cause multiphoton phenomenon state, thereby breaking
Si--O--Si bonds of quartz crystal in the region to form voids in
the region, and (b) peeling the thin quartz crystal wafer from a
body of the quartz crystal block along the voids.
[0012] According to the present invention, the stealth dicing
technique is applied to a quartz crystal block for manufacturing
thin quartz crystal wafers with high productivity. The steps (a)
and (b) may be repeatedly carried out on the quartz crystal block
from which the thin quartz crystal wafer has been peeled, for
thereby peeling a plurality of thin quartz crystal wafers
successively from the principal surface of the quartz crystal
block. According to this process, quartz crystal wastes may be
reduced, and the productivity may further be increased. The
principal surface of the quartz crystal block may be polished after
the thin quartz crystal wafer has been peeled therefrom, and the
step (a) may be carried out on the quartz crystal block. The laser
beam may thus be well transmitted into the quartz crystal block,
allowing the process of peeling off thin quartz crystal wafers
successively from the quartz crystal block to be carried out
better.
[0013] Each of the thin quartz crystal wafers thus obtained may be
divided into individual crystal blanks for use in crystal units.
Using such crystal blanks, crystal units can be produced
inexpensively.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1A, 1B, and 1C are perspective views illustrative of a
conventional process of manufacturing a thin quartz crystal
wafer;
[0015] FIG. 2 is a plan view of a conventional crystal blank;
[0016] FIG. 3A is a perspective view illustrative of a method of
manufacturing a thin quartz crystal wafer according to the present
invention;
[0017] FIG. 3B is a plan view illustrative of the method of
manufacturing a thin quartz crystal wafer according to the present
invention; and
[0018] FIG. 4 is a plan view of a crystal blank.
DETAILED DESCRIPTION OF THE INVENTION
[0019] A method of manufacturing a thin quartz crystal wafer
according to a preferred embodiment of the present invention will
be described below.
[0020] According to the embodiment, as shown in FIG. 3A, thin
quartz crystal wafer 1 is cut from quartz crystal block 2 in the
form of a rectangular parallelepiped having flat surfaces. AT-cut
quartz crystal blanks are produced from thin quartz crystal wafer
1. As shown in FIG. 3A, quartz crystal block 2 is cut from a
crystal body (not shown) of synthetic quartz crystal along X-, Y'-,
and Z'-axes of quartz crystal. Specifically, quartz crystal block 2
has six surfaces including a pair of XZ' surfaces, a pair of XY'
surfaces, and a pair of Y'Z' surfaces. If the XZ' surfaces of quart
crystal block 2 are regarded as principal surfaces, then these
principal surfaces are first polished to a mirror finish.
[0021] Then, while quartz crystal block 2 is moving in the
direction of the Z'-axis, one of the principal surfaces of quartz
crystal block 2 is continuously irradiated with laser beam P
applied in the direction of the Y'-axis. When one cycle of scanning
quartz crystal block 2 with laser beam P in the direction of the
Z'-axis is completed, quartz crystal block 2 is slightly moved in
the direction of the X-axis. Then, while quartz crystal block 2 is
moving in the direction of the --Z'-axis, quartz crystal block 2 is
continuously irradiated with laser beam P. Line D-D in FIG. 3B
represents the path of the beam spot of laser beam P on the
irradiated principal surface of quartz crystal block 2 in one cycle
of scanning quartz crystal block 2 with laser beam P in the
direction of the Z'-axis. Laser beam P is focused or converged by a
lens system (not shown) at a position within quartz crystal block 2
which is about 25 .mu.m deep from the principal surface of quartz
crystal block 2. Laser beam P is of a wavelength that is
transmissive with respect to quartz crystal and is capable of
breaking Si--O--Si (silicon-oxygen-silicon) interatomic bonds in
quartz crystal by way of multiphoton absorption.
[0022] As a result, multiphoton absorption occurs due to the
convergence of laser beam P in a region within quartz crystal block
2 which is about 25 .mu.m deep from the principal surface of quartz
crystal block 2, locally breaking Si--O--Si interatomic bonds of in
quartz crystal. The broken interatomic bonds produce an optically
damaged state, forming voids along the path of laser beam P in
quartz crystal block 2. Since quartz crystal block 2 is moving
along the Z'-axis and the X-axis, a number of voids are clustered
in quartz crystal block 2 along a plane that is about 25 .mu.m deep
from the principal surface of quartz crystal block 2.
[0023] Thereafter, the principal surface of quartz crystal block 2
is applied to a fixture base such as a glass plate or the like by
optical bonding or the like, and then heated to expand, activate,
and explode the voids formed in quartz crystal block 2. The
clustered voids are joined together along the plane, fully
destroying interatomic bonds between a main body of quartz crystal
block 2 and a surface layer (which will become thin quartz crystal
wafer 1). As a result, the surface layer is peeled off the main
body of quartz crystal block 2, producing thin quartz crystal wafer
1 having a thickness of about 25 .mu.m.
[0024] After thin quartz crystal wafer 1 has been obtained, the
principal surface of quartz crystal block 2 from which thin quartz
crystal wafer 1 has been peeled is polished. Then, while quartz
crystal block 2 is being scanned in the directions of the Z'-axis
and the X-axis, laser beam P is converged at a position that is
about 25 .mu.m deep from the principal surface of quartz crystal
block 2 to cause multiphoton phenomenon state. Voids are now formed
in quartz crystal block 2 by multiphoton absorption, and then
quartz crystal block 2 is heated to peel off next thin quartz
crystal wafer 1. The above process is repeated to obtain a number
of thin quartz crystal wafers 1 successively from quartz crystal
block 2.
[0025] Then, opposite principal surfaces of each of thin quartz
crystal wafers 1 are polished until thin quartz crystal wafer 1 has
a desired thickness. Thereafter, exciting electrodes 5 and
extension electrodes 6 are integrally formed on both the principal
surfaces of each of regions of thin quartz crystal wafers 1 which
is to serve as a crystal blank. As shown in FIG. 4, on the end of
the region which corresponds to each crystal blank and to which
extension electrodes 6 extend, electrode layers serving as part of
extension electrodes 6 are disposed on both principal surfaces.
These electrode layers on both principal surfaces are electrically
connected to each other via through-holes 7 defined in thin quartz
crystal wafer 1. Thereafter, thin quartz crystal wafers 1 is
divided into individual crystal blanks by a machining process using
a wire saw or a blade saw. In this manner, a number of crystal
blanks 4 as shown in FIG. 4 are obtained from each of thin quartz
crystal wafers 1.
[0026] According to the manufacturing method described above, since
thin quartz crystal wafer 1 is produced by using stealth dicing
technology and applying a laser beam to the principal surface of
quartz crystal block 2, thin quartz crystal wafer 1 can directly be
obtained from quartz crystal block 2, rather than from a thick
quartz crystal wafer which would otherwise need to be produced from
quartz crystal block 2. Accordingly, the amount of quartz crystal
that is wastefully ground off is highly reduced, and hence any
quartz crystal wastes are minimized. For example, if a thin quartz
crystal wafer having a thickness of 18 .mu.m (corresponding to a
resonant frequency of 100 MHz in case of an AT-cut crystal blank)
is obtained from a conventional thick quartz crystal wafer having a
thickness of 350 .mu.m, then an amount of quartz crystal which
corresponds to a thickness of 332 .mu.m is wasted. According to the
present embodiment, however, because a laser beam is converged at a
depth of 25 .mu.m from the principal surface of a quartz crystal
block to peel a thin quartz crystal wafer from the quartz crystal
block and the thin quartz crystal wafer is polished to a thickness
of 18 .mu.m, only an amount of quartz crystal which corresponds to
a thickness of 7 .mu.m is wasted. Consequently, the manufacturing
method according to the present invention is 47 times more
efficient than the conventional manufacturing process, and hence is
highly productive.
[0027] According to the present embodiment, after one thin quartz
crystal wafer 1 is peeled off quartz crystal block 2, the principal
surface of quartz crystal block 2 is polished again, and the laser
beam is applied to quart crystal block 2. Therefore, the laser beam
can reliably be transmitted into quartz crystal block 2, and thin
quartz crystal wafers 1 can successively be obtained from quartz
crystal block 2. Each of thin quartz crystal wafers 1 is then
divided into individual crystal blanks 4. Consequently, crystal
units can be produced inexpensively. Extension electrodes 6 are
formed on both principal surfaces of regions of thin quartz crystal
wafer 1 which correspond to respective crystal blanks, and are
electrically connected to each other via through holes 7. As a
result, extension electrodes 6 can extend from one to the other of
the principal surfaces of regions of thin quartz crystal wafer 1
before they are divided. According to the present embodiment,
therefore, crystal units can be assembled immediately after thin
quartz crystal wafer 1 is divided into crystal blanks.
[0028] The present invention is not limited to the preferred
embodiment which has been described above, but various changes or
modifications may be made therein.
[0029] For example, when laser beam P is applied to quartz crystal
block 2 it may be intermittently applied not only in the direction
of the X-axis, but also in the direction of the Z'-axis. In the
above embodiment, after an optically damaged state is produced in
quartz crystal block 2 by making the multiphoton phenomenon state,
quartz crystal block 2 is heated to peel thin quartz crystal wafer
1 therefrom. However, rather than heating quartz crystal block 2,
quartz crystal block 2 may be immersed or dipped in an etching
solution to chemically peel thin quartz crystal wafer 1
therefrom.
[0030] Furthermore, after each thin quartz crystal wafer is divided
into individual crystal blanks, excitation electrodes and extension
electrodes may be formed on each of the crystal blanks.
* * * * *